Hitherto, in aqueous solution systems it is known to use a curtain coating method comprises simultaneously applying silver halide emulsions containing gelatin as a binder using a slide hopper coating apparatus to form a multilayer photographic film or paper. A moving web is coated by a free falling curtain of coating composition wherein a multilayer composition is formed on the slide hopper and caused to impinge onto an object or moving web to form a coated layer thereon. The formation of a composite of a plurality of distinct layers on a moving web is described in Hughes U.S. Pat. No. 3,508,947 issued on Apr. 28, 1970 which relates particularly to the manufacture of multilayer photographic materials such as photographic film and paper.
U.S. Pat. No. 3,508,947 describes a method commonly used to start-up a continuous curtain coating process. A flat curtain deflector is mounted so it can be pivoted or slid into position. During preparation for coating the deflector diverts the free fall of the curtain fluids to flow down the deflector surface into a catch basin. The coating process is started after establishing the stability of the curtain and bringing the web to a normal coating speed. The curtain defector is then retracted by pivoting or sliding it away from the falling curtain to allow the curtain to impinge onto the moving web. The curtain deflector can be located on either the front or back side of the falling curtain. Use of a deflector in this manner results in the accumulation of excess coating liquids on the moving web.
Accumulation of excess coating liquids on the moving web often occur in amounts that result in the generation of large quantities of extremely costly waste, e.g., for each occurrence it is not unusual to have more than a thousand linear meters of wasted coated photographic material.
In addition areas of excessive coating liquids deposited on the web support will often transfer from the web onto the machine rolls used in transporting the moving web and in the wind up end of the machine. Significant operating cost result when the coating process must be stopped to clean the coating machine. Furthermore, it should be appreciated that each new start of a coating process is susceptible to incurring the same problems.
Efficient use of the curtain coating method for manufacturing photographic materials has thus far been adversely effected by the inability to develop efficient coating starts at the intended coating flow rate and web speeds without depositing areas of excessive coating liquid on the web support. Although curtain flow rates and web speeds can be adjusted to reduce contamination of the web transport rolls and coated product, the problem of accumulation of excess coating liquids still exists to a very undesirable extent.